Hair Pulling Triggers One of the Quickest Known Pain Responses

CHICAGO — Big news for fighting sisters: Scientists have found the sensors that signal the painful zing of a hair pull. And this pain message can rip along a nerve fiber at about 100 miles an hour, placing it among the fastest known pain signals.

The discovery, presented October 8 at the annual meeting of the Society for Neuroscience, offers insight into the diverse ways our bodies sense and respond to different sorts of pain.

Pain can come from many catastrophes — cuts, jabs, pinches, cramps, bites, slaps, stubbing a toe in the dark. And while our bodies can generally tell these insults apart thanks to a variety of biological pathways, they all hurt. “It’s not surprising that we have figured out many, many ways to make [pain] happen,” says neuroscientist Gregory Dussor of the University of Texas at Dallas. “Because when it doesn’t, we don’t live.”

Laboratory tests showed a hair pull to be about 10 times as painful as a pinprick, neuroscientist Emma Kindström of Linköping University in Sweden and colleagues found. The pain of the pull relies on a large, propeller-shaped protein called PIEZO2, further tests showed. That sensor was known to detect mechanical forces, including light touches, but wasn’t thought to detect acute pain signals. People who lack this protein don’t feel hair-pull pain. A hair-pull signal moves along nerve fibers much faster than other sorts of pain, Kindström says, traveling in bursts along an insulated conduit called an Aβ nerve fiber. Other kinds of pain signals, such as a burn from a hot stove, travel more slowly along different kinds of fibers.

People probably vary in their pain responses to hair pulls, she says. “Some people enjoy taking a very, very hot shower, while some people find it very painful. I don’t see why hair pulling would be different.” She sees variability in her pet dogs. Harry, her white Pomeranian, doesn’t mind getting brushed. But Norton, her Chihuahua, is very sensitive to fur pulling, so he inflicts pain back, with a bite.